=Moss
(Bryophyte)
=


external image GREEN-carpet-of-MOSS.jpg

Green Surface of Moss (SM)


Classification/Diagnostic Characteristics:

Moss, part of the Bryophyta clade, are a part of the much larger grouping of Land Plants. Plants in the bryophyte clade are spore-producing, rather than seed-producing, plants that do not grow flowers. Found on soil, rock, tree trunks, leaves, rotting wood, and bones, they do not have true roots, but instead have rhizoids that are used as an anchor as they do not actually extract nutrients or water. Unique from the other two types of plants in the Bryophyta clade, liverwort and hornwort, a moss plant grows on soil and shows a tufty growth habit, especially in a dry, exposed location (11). Moss are known as nonvascular land plants because they lack tracheids, however, common characteristics of mosses show that they have a filamentous stage, and sporophyte grows from the top.


Phylogenetic_red.jpg

This phylogenetic tree shows the evolution of land plants and how moss factors in. (16) (LK)


Moss is a Phylum that consists of many classes.

Kingdom: Plantae

Division: Bryphyta

Classes: Takakiopsida, Sphagnopsida, Andreaeopsida, Andreaeobryopsida, Oedipodiopsida, Polytrichopsida, Tetraphidopsida, Bryopsida

(SL 19)


Relationship to Humans:

Moss is not as economically important when compared to other plants, but the Sphagnum moss is useful to humans. In its natural habitat, the Sphagnum moss will selectively absorb certain ions and secrete other ions. The bog where it normally lives and grows in will turn acidic and anaerobic over time. The decomposition rate of the bog by bacteria is very slow. Organisms that have been buried in Sphagnum bogs remain very well preserved for a long period of time. Gardeners also commonly use Sphagnum. Some gardeners mix dried Sphagnum or peat moss with soil to improve the soils water holding capacity. In Sphagnum bogs, American white cedars often grows which can be used for making shingles for a house. Sphagnum moss also has antiseptic properties and can hold up to 20 times its own weight in water.


During the Russo-Japanese war and World War I Sphagnum moss was used as a bandage for soldier. Using moss during the war would save cotton for making gun powder. Peat is derived largely from Sphagnum and is important as a fossil fuel, especially in Scotland and Ireland. In Scotland, Sphagnum moss has an important role in the making of scotch whiskey. It is important because many scotches are made from grains that are steeped in the water from a Sphagnum bog during the malting procedure. Also after the malting procedure, the malted grains are boiled over a fire of burning Sphagnum peat imparting a characteristic flavor and aroma to the scotch whiskey. Their is also a negative to all the peat moss harvesting. The process of peat harvesting includes draining the Sphagnum bog which is a adverse because it is an loss of valuable wetland. Peat harvesting has recently increased since it was discovered that it could be used as a natural oil absorbent to clean up oil spills. Concerned environmentalists created codes for harvesting peat, so the resource will remain sustainable (1). (SM)


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Habitat and Niche:

Mosses are found in many different environments, but often on cool ground that remains damp, where they can create thick mats.


Mosses are renowned for their ability to live almost anywhere in the world including tropical forests, temperate forests, in lakes, on rocks, submerged in sea water, and in the Arctic Circle. These non-vascular land plants success has been largely attributed to the relatively few requirements needed for growth which include a stable substratum (for attachment), adequate sunlight, sufficient moisture, a favorable temperature, and (for best growth) a humid atmosphere.(5) A select few mosses also posses the ability to endure long periods of freezing or dehydration by halting photosynthesis and resuming the process once the suitable environment has returned.(6)


In all of its environments, mosses fill the role of a decomposer and are crucial in the process known as nutrient cycling, or the returning of nutrients locked in deceased organisms to the community at large.(5)(SF)


Mosses lack central vascular tissue, or a system to transport fluids and nutrients throughout the organism, which explains why mosses grow to be short. Furthermore, these organisms are typically confined to a location to their immobility. One way they are able to distribute is by the dispersion of haploid moss spores (essentially pre-mature mosses containing one set of chromosomal DNA) due to wind and water. This explains why mosses are prevalent throughout the world in places we would not expect. (7) (SR)


Predator Avoidance:

Because mosses are typically immobile and exposed, they do not have major structural or behavioral adaptations to fend off predators. This organism compensates for this setback in a couple of ways. One, it has employed both sexual and asexual means of reproduction to produce offspring in different circumstances. This allows for a positive, stable growth rate and allows the organism to thrive in critical conditions. Next, many mosses, have adapted to appear unnoticeable or camouflaged. This helps to conceal the plant from organisms such as deer, caribou and owls. (SR)


Nutrient Acquisition:

Since mosses are typically quite small and do not have a vascular system to transport water and minerals throughout the organism, mosses grow to allow diffusion of minerals across the surface of the body, allowing for minerals to be transported and received throughout the moss body. Some moss gametophytes are very large, and therefore cannot transport water throughout their bodies. These particular mosses contain a cell called a hydroid, whose purpose is to die and leave a channel for water travel. It's purpose and function is similar to that of a tracheid, but it does not have the lignin and the cell-wall structure. Although mosses are considered nonvascular plants, that can be misleading because they do have a simple system of internal transport.


Moss hydroids are typically referred to as central strands, and when observed under a microscope, hydroids are distinguished by the appearance of a hollow center to the stem of the moss. Because hydroids have thin cell membranes, they deteriorate at a relatively frequent rate, creating this hollow appearance. (AC) (18)


external image centralstrand.jpg


Reproduction and Life Cycle:

The life cycle of nonvascular plants, specifically mosses, are dependent on liquid water. The cycle starts with a sporophyte producing unicellular haploid sporesby meiosis within a sporangium. When those spores germinate, it creates a multicellular haploid gametophyte which contains chloroplasts and are therefore, photosynthetic. These gametes eventually form within specialized sex organs, which are referred to as the gametangia. Specifically, thearchegonium is the female sex organ and the antheridium is the male sex organ. Both sex organs are produced on the same individual, typically adjacent individuals fertilize one another's gametes, which allows for genetic diversity.


Once released from the female sex organ, the male sperm must swim or be splashed by raindrops to a nearby male sex organ, which proves the important of water in this reproductive life cycle. The sperm are helped by chemical attractants released by the egg, however, before the sperm can complete the journey, certain cells in the male sex organ must break down to create a water-filled canal in which the sperm completes its journey in. Once sperm reaches the egg, the nucleus of the sperm fuses with the egg nucleus, which then forms a diploid zygote. The zygote then divides through mitosis which creates a multicellular, diploid sporophyte embryo. The sporophyte eventually matures and produces sporangium, where meiotic divisions produce spores, which are then the start of the next gametophyte generation.


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After beginning its life cycle as a haploid spore, moss germinates and produces the thin, felt-like layer of vegetation that typically comes to mind when picturing moss, known as the protonema, or in some cases the thallus. In this phase, the moss is composed of interweaving filaments and fibers. The protonema then develops the gametophores discussed in the previous sections, often growing multiple gametophore shoots in one clump. (YR) (14)



Moss bud protonema.jpg


Growth and Development:

All life cycles of land plants contain an alteration of generations, meaning the life cycle includes both a multicellular haploid stage and a multicellular diploid stage.


Nonvascular plants do not have leaves, stems, and roots, although they have analogous structures to each. Water can move through the mats by capillary action, leaf like structures catch and hold water.

A germinated spore will form into a rhizoid. From the rhizoid a bud will form and grow into a gametophyte with both sex organs that will fertilize into an embryo and eventually sporophyte with a sporangium that releases ungerminated spores. (SM) [12]


Integument:

Land plants have many different examples of integument, which helps them survive on land rather than an aquatic environment. Most have a cuticle, which is a waxy coating of lipids that slows water loss. Moss specifically have gametangia which are multicellular organs that enclose plant gametes and prevents them from drying out.


Movement:

Moss tend to spread out as far as they can on the surface they are living on in order to get the largest amount of surface area possible for water transport from the environment into the organism.


Moss is incapable of movement as it is a plant. The way it spreads is through spores which are dispersed by the wind. In some cases the acceleration of the spores can exceed 36000 times the acceleration of gravity.

(SM) [9]


In terms of growth patterns/movement, the two different types of moss (with respect to genital locations on the plant) exhibit different behaviors. Acrocarpous mosses, whose female sex organs are located at the ends of stems, tend to grow slowly and cluster in colonies. They are also more likely to be susceptible to invasion by weeds, but are also less quick to re-form from a fragmented states. Pleurocarpous mosses, whose female genitalia are in short, wide branches, propagate in a web-like manner from the central colony. They tend to form carpet-like formations, instead of the vertical "lumps" seen in acrocarpous mosses. They also regenerate from fragments relatively quickly, and are able to easily attach to surfaces like stone, making them compatible with hard surfaces. (SS-10).


Sensing the Environment:

Moss, like most green-plants, are autotrophic organisms. To sustain this sort of lifestyle, they require a pigment called chlorophyll which absorbs the sunlight needed to conduct photosynthesis. This relates back to why moss needs to grow in areas that are both damp and sunlight-abundant, because they manufacture their own food and lack vascular transportation for water. (SM)


Gas Exchange:

Mosses have stomata, which are very important for water retention and gas exchange. A pair of cells called guard cells control the opening and closing of the stomata. Below is a picture of how guard cells work (4). (SP)



external image Stomata_6.jpg

Waste Removal:

As simple nonvascular plants, mosses only have a few mechanisms in which they can exchange and remove nutrients. They use simple diffusion and stomata in order to transfer and remove wastes and nutrients.


Environmental Physiology:

Most mosses need to live in a damp or moist environment, so that they can diffuse water and nutrients throughout their body. Typically these areas are cool as well. Other than that, mosses are pretty versatile, they can live in a variety of different places, including across continents and different terrestrial environments. A few nonvascular plants live in fresh water, however, none live in the ocean, which probably means mosses cannot survive in environments of high salinity.


Mosses also need a surrounding of liquid water to reproduce. In addition, mosses have a certain level of shade tolerance, and, in general, mosses like shady regions because the environment is more damp. Mosses are sensitive to pH levels, and squeezing a lime on moss will inhibit its growth. Mosses like to inhabit smooth, damp surfaces, which are often found around streams, and do not inhabit rough, rocky surfaces. (20) (RS)


Waterfall_over_moss_by_Rhube.jpg


Internal Circulation:

Mosses must transfer water and nutrients throughout the body on its own because it does not have a vascular system with tracheids. This means most nonvascular plants use capillary action to circulate nutrients and water throughout the body along with simple diffusion.


As nonvascular plants, mosses lack a xylem to transport water and a phloem to transfer to nutrients. This lack of a system that is able to direct substances to specific parts of the body means that mosses lack any sort of internal means to deal with the transportation over a long distance, as they must rely on diffusion. As such, mosses generally grow to be very small, only one to two centimeters tall, because they must be able to guarantee that all parts of the plant will receive the necessary nutrients and water to survive. Rather than grow tall, mosses grow wide and cover surface area horizontally. (17) (CM)


Chemical Control:

Plant hormones play a role in regulation, growth, and development.

1. Cytokinins:

  • Stimulates cell division.
  • Stimulates morphogenesis (shoot initiation/bud formation) in tissue culture.
  • Stimulates the growth of lateral buds-release of apical dominance.
  • May enhance stomatal opening in some species.

Gibberellins:

  • Stimulate stem elongation by stimulating cell division and elongation.
  • Breaks seed dormancy in some plants which require stratification or light to induce germination.
  • Stimulates enzyme production (a-amylase) in germinating cereal grains for mobilization of seed reserves.

(SM) [13]


Photoreceptors are pigments that are associated with proteins. Light turns on these photoreceptors which regulate development processes that involve light responses (the process of photosynthesis: the light dependent (dark reactions) and independent phase (Calvin cycle), where many chemicals built by the plant and taken in by the plant are used for processing to form glucose (C6H12O6)). (SM)



Review Questions:

1.How do the sporophyte and gametophyte of moss compare to those of other species of plants? (SM)

2. Explain how moss reproduce and why it allows them to live in such diverse habitats. (LK)

3. How does moss utilize cytokinins and gibberellins? (JM)

4. What sets the bryophyte clade apart from other plants? (JM)

5. Describe how large moss gametophytes transport water through its system (NU)

6. How are mosses similar and dissimilar to flowering plants? Trees? Fungi? (RG)

7. Moss is not a species. Explain how the Phylum moss encompasses a broad array of plants, and what distinguishes a moss from another plant. (SL)


Sources:

1. Ensminger, Peter A. "Moss - Importance To Humans." - Sphagnum, Peat, Bogs, and Plant. N.p., n.d. Web. 24 Nov. 2013.

2. Sphagnum Bog picture

3. Fertilizer picture

4. "Transport in Plants." Transport in Plants. N.p., n.d. Web. 16 Nov. 2013.

5."Nutrition." //Encyclopedia Britannica Online//. Encyclopedia Britannica, n.d. Web. 25 Nov. 2013.

6."MossBasicsText." //MossBasicsText//. N.p., n.d. Web. 25 Nov. 2013

7. http://www.hiddenforest.co.nz/bryophytes/mosses/reproduction.htm

8. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.

9. http://www.wisegeek.com/how-can-i-grow-moss.htm

10. http://www.mossandstonegardens.com/blog/how-to-grow-moss

11. http://www.anbg.gov.au/bryophyte/what-is-bryophyte.html

12. http://biology.clc.uc.edu/courses/bio106/mosses.htm

13. http://www.plant-hormones.info/index.htm

14. http://www.microview.org.uk/millennium/pages/moss_lifecycle.htm

15.http://botit.botany.wisc.edu/Resources/Botany/Bryophytes/Mosses/protonema/Moss%20bud%20protonema.jpg

16. Phylogenetic Tree

17. "Nonvascular Plants." Nonvascular Plants. N.p., n.d. Web. 25 Nov. 2013.

18. Kellman, Ken. "Hydroids in the Moss Stem and Leaf." Discussions in Western Bryology. University of California Berkeley, n.d. Web. 25 Nov. 2013.

19.http://www.uniprot.org/taxonomy/?query=moss&sort=score

20. "Ecology of Moss." Ecomare, n.d. Web. 25 Nov. 2013.

21. Rhube. Waterfall over Moss. Digital image. Deviantart, n.d. Web. 25 Nov. 2013.